A set of twins who were the world's first people to be born after genetic editing could die early.
The Chinese scientist who altered their DNA has been criticised, with his actions being described as "dangerous" and "foolish".
Prof He Jiankui carried out the work while they were embryos to try to protect them from HIV.
He targeted the CCR5 gene, which relates to the immune system and plays a role in how HIV infects cells, using gene-editing technology.
The baby girls, known as Nana and Lulu, were born last year.
Now a US study has found that his work may have inadvertently shortened the girls' lifespans.
Researchers at the University of Berkley in California analysed 410,000 people and found that those who were naturally born with the CCR5 were 20 per cent more likely to die before the age of 78.
"In this case, it is probably not a mutation that most people would want to have," Prof Rasmus Nielsen, from UC Berkeley, told
BBC News.
"You are actually, on average, worse off having it."
Controversy
News of Prof Jiankui's work was met with
widespread criticism last year, particularly as he had worked on two perfectly healthy embryos.
Questions about the ethics of genetic editing were also raised.
There is some concern that if the process becomes widespread, future generations will breed out certain characteristics and over-focus on aesthetics, creating so-called 'designer babies'.
Announcing the babies' birth last year, Prof Jiankui said that he recognises that his work is "controversial" but that he believed that "families need this technology."
